Summary Nigral dopaminergic (DA) neurons (i.e. A9 DA neurons) that are lost in Parkinson?s disease (PD) have autonomous pacemaking action potentials, massive axon arborization, and expression of GIRK2, but not calbindin. Despite the significant progress in the differentiation of human embryonic stem cells (hESCs) to midbrain DA neurons, it has been difficult to generate A9 type DA neurons, particularly from human induced pluripotent stem cells (iPSCs). We developed an improved floorplate-based method to differentiate patient-specific iPSCs to midbrain DA neurons that expressed appropriate markers for A9 type cells and exhibited calcium channel-dependent autonomous pacemaking activities independent of glutamatergic inputs. These iPSC-derived DA neurons extended elaborate neuronal fibers when grafted to 6- OHDA-lesioned rats and restored locomotor deficits. We have generated isogenic pairs of iPSCs by repairing parkin mutations in patient cells and by introducing parkin mutations to control cells. Using these isogenic iPSCs, we will study how parkin mutations mechanistically disrupt the precision of dopaminergic transmission in three different preparations: monolayer cultures, brain organoids, and graft in 6-OHDA-lesioned rat brains. The three novel approaches will enable us to approximate the situation in the brains of PD patients. The study will bridge the gap between mechanistic understanding of the cellular function of parkin and its role in PD pathophysiology that is directly linked to the motor symptoms. The results will stimulate the development of disease-modifying therapies of Parkinson's disease .